NPI Number structure

NPI is using only "1" and "2" for now

In answer to a question about whether "3" and "4" might be encountered as the first digit of NPI, the following is my understanding. I want to emphasize that this is only my understanding. We may be able to get confirmation from the NPPES developers but it is probably not necessary for most editing logic.

1. The NPPES initial specs were that NPI would be in the number space of "1000000000" through "4999999999". That is, NPI would begin with "1", "2", "3", or "4". We call those rows.

2. The theoretical capacity of each row is 100 million NPIs. However, the NPPES system is using about 1/3rd of the possible NPI numbers; so the effective capacity of each row is 33 million.

3. The NPPES system assigns new NPIs sequentially beginning in the "1" row, skipping about 2 possible numbers for each one assigned. Say the initial use of NPIs to enumerate all the providers is 4 million with 20% wastage; that would use 4.8 million numbers. Say the annual new NPI usage is 6% (of 4 million), and that would be 240,000 new NPIs per year. So it should take about 100 years to use up the "1" row.

4. Assuming correct assumptions and fault-free operation of NPPES, I think we won't see "3" or "4" for a long time. I'll probably be retired by then.